Quarterly Supplementary Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 1,312	$ 1,402	$ 1,371	$ 1,364	$ 1,263	$ 1,278	$ 1,316	$ 1,285	$ 5,449	$ 5,142	$ 4,945
Income before income taxes	128	253	166	265	216	243	248	174	812	881	721
Net Income (Loss) Attributable to Parent	$ 100	$ 180	$ 123	$ 188	$ 156	$ 174	$ 176	$ 128	$ 591	$ 634	$ 525
Basic (in usd per share)	$ 0.61	$ 1.09	$ 0.75	$ 1.14	$ 0.95	$ 1.06	$ 1.07	$ 0.78	$ 3.59	$ 3.87	$ 3.21
Diluted (in usd per share)	$ 0.60	$ 1.08	$ 0.74	$ 1.13	$ 0.94	$ 1.05	$ 1.06	$ 0.77	$ 3.55	$ 3.83	$ 3.18